4,884 research outputs found
Quantum computational renormalization in the Haldane phase
Single-spin measurements on the ground state of an interacting spin lattice
can be used to perform a quantum computation. We show how such measurements can
mimic renormalization group transformations and remove the short-ranged
variations of the state that can reduce the fidelity of a computation. This
suggests that the quantum computational ability of a spin lattice could be a
robust property of a quantum phase. We illustrate our idea with the ground
state of a spin-1 chain, which can serve as a quantum computational wire not
only at the Affleck-Kennedy-Lieb-Tasaki point, but within the
rotationally-invariant Haldane phase.Comment: v2: 4 pages, 3 figures; improved description of buffering scheme and
connection to string operators. v3: final published versio
Traces of Thermalization from Transverse Momentum Fluctuations in Nuclear Collisions
Scattering of particles produced in Au+Au collisions at RHIC can wrestle the
system into a state near local thermal equilibrium. I illustrate how
measurements of the centrality dependence of the mean transverse momentum and
its fluctuations can exhibit this thermalization.Comment: 4 pages, 2 eps figures, final version to appear in PR
Simulation of braiding anyons using Matrix Product States
Anyons exist as point like particles in two dimensions and carry braid
statistics which enable interactions that are independent of the distance
between the particles. Except for a relatively few number of models which are
analytically tractable, much of the physics of anyons remain still unexplored.
In this paper, we show how U(1)-symmetry can be combined with the previously
proposed anyonic Matrix Product States to simulate ground states and dynamics
of anyonic systems on a lattice at any rational particle number density. We
provide proof of principle by studying itinerant anyons on a one dimensional
chain where no natural notion of braiding arises and also on a two-leg ladder
where the anyons hop between sites and possibly braid. We compare the result of
the ground state energies of Fibonacci anyons against hardcore bosons and
spinless fermions. In addition, we report the entanglement entropies of the
ground states of interacting Fibonacci anyons on a fully filled two-leg ladder
at different interaction strength, identifying gapped or gapless points in the
parameter space. As an outlook, our approach can also prove useful in studying
the time dynamics of a finite number of nonabelian anyons on a finite
two-dimensional lattice.Comment: Revised version: 20 pages, 14 captioned figures, 2 new tables. We
have moved a significant amount of material concerning symmetric tensors for
anyons --- which can be found in prior works --- to Appendices in order to
streamline our exposition of the modified Anyonic-U(1) ansat
Draft genome sequence of the Streptococcus pneumoniae Avery strain A66
We have used HiSeq 2000 technology to generate a draft genome sequence of Streptococcus pneumoniae strain A66. This is a common study strain used in investigations of pneumococcal bacterium-host interactions and was used in the seminal genetic studies of Avery et al
On fault-tolerance with noisy and slow measurements
It is not so well-known that measurement-free quantum error correction
protocols can be designed to achieve fault-tolerant quantum computing. Despite
the potential advantages of using such protocols in terms of the relaxation of
accuracy, speed and addressing requirements on the measurement process, they
have usually been overlooked because they are expected to yield a very bad
threshold as compared to error correction protocols which use measurements.
Here we show that this is not the case. We design fault-tolerant circuits for
the 9 qubit Bacon-Shor code and find a threshold for gates and preparation of
(30% of the best known result for the
same code using measurement based error correction) while admitting up to 1/3
error rates for measurements and allocating no constraints on measurement
speed. We further show that demanding gate error rates sufficiently below the
threshold one can improve the preparation threshold to .
We also show how these techniques can be adapted to other
Calderbank-Shor-Steane codes.Comment: 11 pages, 7 figures. v3 has an extended exposition and several
simplifications that provide for an improved threshold value and resource
overhea
Quantum Operation Time Reversal
The dynamics of an open quantum system can be described by a quantum
operation, a linear, complete positive map of operators. Here, I exhibit a
compact expression for the time reversal of a quantum operation, which is
closely analogous to the time reversal of a classical Markov transition matrix.
Since open quantum dynamics are stochastic, and not, in general, deterministic,
the time reversal is not, in general, an inversion of the dynamics. Rather, the
system relaxes towards equilibrium in both the forward and reverse time
directions. The probability of a quantum trajectory and the conjugate, time
reversed trajectory are related by the heat exchanged with the environment.Comment: 4 page
Radon as an anthropogenic indoor air pollutant as exemplified by radium dial watches and other uranium- and radium- containing artefacts
Radon is generally regarded as a naturally occurring radiological hazard but we report here measurements of significant, hazardous radon concentrations that arise from man-made sources, e.g. radium-dial watches. This study is an examination and assessment of health risks from radium and uranium found in historical artefacts, and the radon that emanates from them. This includes radium-dial watches, the main focus, plus clocks, aircraft instruments, and ornaments and artefacts made of uranium glass / uranium-glazed. Such objects were very popular in the 1930s and 1940s and are still readily available today.
A collection of 30 radium-dial pocket and wrist watches was measured and shown to be capable of giving rise to radon concentrations two orders of magnitude greater than the UK Domestic Action Level of 200 Bq•m-3 in unventilated or poorly ventilated rooms. Furthermore, individual watches are capable of giving rise to radon concentrations in excess of the UK Domestic Action Level. We also highlight a gap in remediation protocols, which are focused on preventing radon entering buildings from outside, with regard to internally-generated radon hazards. Radon as arising from man-made objects such as radium-dial watches should be considered appropriately in radon protocols and guidelines
The production of a non-homogeneous classical pion field and the distribution of the neutral and charged pions
The probability distribution as a function of the ratio
of the neutral to total multiplicities is calculated for the
classical pion fields quickly varying in space and time.Comment: 6 pages, 1 .eps figure, using epsfig, submitted to Phys.Let
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